Bone fixation methods

ABSTRACT

A bone fixation plate includes a first opening formed in a plate that is configured to receive a first fastener; a second opening formed in the plate that is configured to receives a second fastener, and a retention member that extends into a third opening formed in the plate between the first opening and the second opening, wherein the retention member is elastically deformable between at least three positions.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.13/010,392 filed Jan. 20, 2011.

FIELD

The present disclosure generally relates to the field of spinalorthopedics, and more particularly to methods and systems for bonefixation plates for vertebrae.

BACKGROUND

The spine is a flexible column formed of a plurality of bones calledvertebrae. The vertebrae include a hollow cavity and essentially stackone upon the other, forming a strong column for support of the craniumand trunk of the body. The hollow core of the spine houses and protectsthe nerves of the spinal cord. The different vertebrae are connected toone another by means of articular processes and intervertebral,fibrocartilaginous bodies. The intervertebral bodies are also known asintervertebral disks and are made of a fibrous ring filled with pulpymaterial. The disks function as spinal shock absorbers and alsocooperate with synovial joints to facilitate movement and maintainflexibility of the spine. When one or more disks degenerate throughaccident or disease, nerves passing near the affected area may becompressed and consequently irritated. The result may be chronic and/ordebilitating back pain due to these spinal disorders.

One procedure for treating spinal disorders involves using substantiallyrigid plates to hold vertebrae in desired spatial relationships andorientations relative to each other. During the procedure, the spine canbe approached anteriorly or posteriorly. In either case, holes aredrilled and tapped in at least two of the vertebrae, to receive screwsor other fasteners used to secure the plate. The holes are accuratelypositioned with reference to openings formed through the plate. In somecases the screws may be self-tapping. Typically the plate is curvedabout its longitudinal axis to facilitate contiguous surface engagementof the plate with the vertebrae. With the plate maintained against thevertebrae, the fasteners are secured within the holes. As a result, theplate maintains the attached vertebrae in a desired spacing andorientation with respect to each other.

One of the problems associated with bone fixation systems and methods isthe tendency of screws or other fasteners to gradually work loose fromthe vertebrae after fixation of the bone plate. Slight shock orvibration of the vertebrae, due to walking, climbing stairs, or morevigorous activity by the patient following treatment increases thistendency, jeopardizing the integrity of fixation. Moreover, as thefasteners work loose, the outward protrusion of the heads over othercomponents of the system can be a source of discomfort and present therisk of trauma to adjacent and surrounding soft tissue.

SUMMARY

A bone fixation plate includes a first opening formed in a plate that isconfigured to receive a first fastener, a second opening formed in theplate that is configured to receives a second fastener, and a retentionmember that extends into a third opening formed in the plate between thefirst opening and the second opening, wherein the retention member iselastically deformable between at least three positions.

In other features, at least one of the first opening and the secondopening is partially blocked by the retention member in at least one ofthe two positions. The third opening is in communication with at leastone of the first opening and the second opening. The three positionsinclude a rest position, a first toggled position, and a second toggledposition.

In yet other features, the retention member blocks at least of a portionof the first opening and the second opening in the rest position. Theretention member elastically deforms away from the first opening whenthe first fastener forces the retention member to the first toggledposition. The retention member deforms away from the second opening whenthe second fastener forces the retention member to the second toggledposition.

A system for bone fixation includes a plate including a first aperture,a second aperture, and an opening between the first and the secondapertures; a retention member extending into the opening of the platethat is elastically deformable from a rest position to first and secondtoggled positions; a first screw including a head configured toelastically deform the retention member to the first toggled position;and a second screw including a head configured to elastically deform theretention member to the second toggled position.

In other features, the retention member further includes an armextending from the plate into the opening and a first projectionextending from the arm into the first aperture. A second projectionextends from the arm into the second aperture.

In yet other features, the first projection blocks a portion of thefirst aperture and the second projection blocks a portion of the secondaperture when the retention member is in the rest position. The firstprojection is inside the opening of the plate when the retention memberis in the first toggled position. The second projection is inside theopening of the plate when the retention member is in the second toggledposition. The first screw forces the first projection away from thefirst aperture in the first toggled position. The second screw forcesthe second projection away from the second aperture in the secondtoggled position.

A method for bone fixation includes the steps of inserting a first screwinto a first aperture of a plate to secure the plate to a vertebra,advancing the first screw to elastically deform a retention memberformed in an opening of the plate, wherein the opening is incommunication with the first aperture, elastically deforming theretention member from a rest position to a first toggled position; andadvancing the first screw until the retention member elastically returnsto the rest position.

In other features, elastically deforming the retention member from therest position to the first toggled position includes flexing an arm ofthe retention member. Advancing the first screw to elastically deformthe retention member includes contacting a projection of the retentionmember with a head of the first screw.

In yet other features, the method further includes the steps ofinserting a second screw into a second aperture of the plate, advancingthe second screw to elastically deform the retention member formed inthe opening of the plate, wherein the opening is in communication withthe second aperture, elastically deforming the retention member from therest position to a second toggled position; and advancing the secondscrew until the retention member elastically returns to the restposition. The first aperture and the second aperture are partiallyblocked when the retention member is in the rest position and one of thefirst and second apertures is partially blocked when the retentionmember is in one of the first toggled position and the second toggledposition.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an elevational view of a bone fixation system attached toadjacent vertebrae according to the principles of the presentdisclosure.

FIG. 2 is an exploded perspective view of the bone fixation systemaccording to the principles of the present disclosure.

FIG. 3 is a top elevational view of the bone fixation plate accordingthe principles of the present disclosure.

FIG. 4 is a bottom elevational view of the bone fixation plate accordingto the principles of the present disclosure.

FIG. 5 is a partial perspective view of a retention mechanism in thebone fixation plate of FIG. 2 according to the principles of the presentdisclosure.

FIGS. 6A-6D are partial cross-sectional views of a portion of the bonefixation plate along line VI of FIG. 3 and a bone screw according to theprinciples of the present disclosure.

FIGS. 7A-7E are partial top elevational views of one end of the bonefixation system as the end is attached to one of the vertebrae.

FIG. 8 is a perspective view of another bone fixation plate according tothe principles of the present disclosure.

FIG. 9 is a top view of another bone fixation plate according to theprinciples of the present disclosure.

DETAILED DESCRIPTION

Some fasteners and bone fixation plates may include retention mechanismsthat may prevent the screws from working loose from the plate andvertebra. However, many retention mechanisms are cumbersome anddifficult to operate during surgical procedures. For example, someplates may have retention mechanisms that include additional hardwareand features such as sliding tabs or projections, springs, and the like.The additional hardware adds weight and complexity to the plates andpresents potential failure modes such as jammed tabs, broken springs, orother failures from the separate moving parts. The additional hardwaremay also require activation by the surgeon. That is, the surgeon may berequired to find the activation point and twist or press a feature onthe screw or plate to activate the retention mechanism. These additionalsteps require additional time and effort by the surgeon who is alreadyunder difficult working conditions such as low light and a confinedsurgical area.

Accordingly, a bone fixation system and method are provided to decreaseweight and complexity while reducing the duration of the surgicalprocedure. The bone fixation plate of the present disclosure includes anintegrated retention mechanism that is formed in the bone fixation plateitself. The retention mechanism includes geometry introduced into thebone fixation plate during the manufacturing process. For example, thegeometry may be introduced by forming the retention mechanism out of amold or cutting with a laser or plasma cutting technique. Thus, theretention mechanism requires no additional hardware on the bone fixationplate. The bone fixation plate of the present disclosure furtherincludes a self-activating retention mechanism that automatically lockswhen a fastener is inserted to attach the plate to a vertebra.

Embodiments of the invention will now be described with reference to theFigures, wherein like numerals reflect like elements throughout. Theterminology used in the description presented herein is not intended tobe interpreted in any limited or restrictive way, simply because it isbeing utilized in conjunction with detailed description of certainspecific embodiments of the invention. Furthermore, embodiments of theinvention may include several novel features, no single one of which issolely responsible for its desirable attributes or which is essential topracticing the invention described herein.

Referring now to FIG. 1, a bone fixation plate 100, hereinafter referredto as the “plate,” is configured to be attached to a first vertebra 300and a second vertebra 400 using bone screws 200. The plate 100 may besubstantially rectangular and include rounded sides and/or contouredsurfaces to facilitate movement of tissue relative to the plate 100after implantation in a patient. The plate 100 includes apertures 104formed in corners of the plate 100. The screws 200 pass through theapertures 104 to attach to the vertebrae 300 and 400. Retentionmechanisms 106, formed between the apertures 104 in the plate 100, keepthe screws 200 from backing out of the vertebrae 300 and 400 afterfixation. A window 108 may also be formed in the plate 100 to provideaccess to the space between the first vertebra 300 and the secondvertebra 400. Although the system and method shown herein may be used tofix together two vertebrae, it is understood that the system and methodmay be applicable to multiple vertebrae in excess of two. For example,the plate 100 may extend beyond the first and/or second vertebra toattach to other adjacent vertebrae and may include additional retentionmechanisms disposed between additional pairs of apertures and screws.

Referring now to FIG. 2, a first screw 200 a may be inserted through afirst aperture 104 a and a second screw 200 b may be inserted through asecond aperture 104 b. A first retention mechanism 106 a is disposedbetween the first and second apertures 104 a and 104 b and is configuredto prevent both the first screw 200 a and the second screw 200 b frombacking out of the plate 100 after fixation to the first vertebra 300.In one embodiment, the first retention mechanism 106 a may be molded ormachined from the material of the plate 100. Thus, the first retentionmechanism 106 a may be integral and continuous with the plate 100. Inother embodiments, the first retention mechanism 106 a may be attachedto the plate 100 between the apertures 104 a and 104 b. The firstretention mechanism 106 a may be attached by welding, snap fit, frictionwelding, or other forms of attachment.

For simplicity, one retention mechanism and one pair of adjacentapertures are discussed in detail herein. However, it is understood byone in the art that the plate 100 of the present disclosure may includeone or more retention mechanisms disposed between any pair of apertures.For example, third and fourth apertures 104 c and 104 d may be mirrorimages of the first and second apertures 104 a and 104 b and configuredto receive third and fourth screws, respectively. Similarly, a secondretention mechanism 106 b may be disposed between the third and fourthapertures 104 c and 104 d. It may be readily understood by one in theart that the second retention mechanism 106 b functions the same as thefirst retention mechanism 106 a with respect to the third and fourthapertures 104 c and 104 d. Thus, each of the retention mechanisms 106 aand 106 b may be referred to hereinafter as simply retention mechanism106. Likewise, each pair of apertures may be referred to hereinafter assimply first and second apertures 104 a and 104 b.

Referring now to FIG. 3, a top view of the plate 100 illustratesadditional features of the retention mechanism 106 and apertures 104 aand 104 b. The first aperture 104 a and the second aperture 104 b areformed in one end of the plate 100. The first and second apertures 104 aand 104 b may be substantially circular and configured to receive thebone screws 200 a and 200 b respectively as shown in FIG. 2. Theretention mechanism 106 is disposed in an opening 110 formed between thefirst and second apertures 104 a and 104 b. The opening 110 may beirregular-shaped to conform to the geometry of the retention mechanism106. In one embodiment, the opening 110 may be in communication withboth the first aperture 104 a and the second aperture 104 b. That is, acontinuous wall is shared between the first aperture 104 a, the secondaperture 104 b, and the opening 110.

The retention mechanism 106 extends from the plate 100 into the opening110 and is configured to lock the bone screws 200 a and 200 b to theplate 100. For example, the retention mechanism 106 may include aflexible arm 112 extending from the plate 100 into the opening 110. Theflexible arm 112 may be attached to the plate at a proximal end 114 andinclude a distal end 116 cantilevered in the opening 110. A firstprojection 118 a extends from the distal end 116 through the opening 110and towards the first aperture 104 a. A second projection 118 b extendsfrom the distal end 116 through the opening 110 towards the secondaperture 104 b. Thus, the retention mechanism 106 may resemble aninverted “T” shaped geometry or a nautical anchor. For example, thefirst and second projections 118 a and 118 b (collectively projections118) may include curvature having a radius approximately equivalent tothe length of the arm 112 from the proximal end 114 to the distal end116.

Referring now to FIG. 4, a bottom view of the plate 100 illustratesadditional features that enable retention of two bone screws with oneretention mechanism 106. Each of the projections 118 a and 118 bincludes a notch 120 a and 120 b respectively (collectively notches120), formed at the ends of the projections 118. The notches 120 permitthe projections 118 to slide over heads of the screws 200 after fixationto the vertebra 300 as described below with reference to FIGS. 6A-6D and7A-7E. The notches 120 may be configured to adjust the strength of theretention mechanism 106 by varying the thickness of the projections 118and/or the arms 112. For example, the notches 120 may decrease thethickness of the retention mechanism 106 and thus increase flexibility.Alternatively, the retention mechanism 106 may be of a uniform thicknessthat permits the projections 118 to slide over heads of the screws 200.

The retention mechanism 106 is capable of elastically moving, bending,or toggling between at least three distinct positions. In a restposition, as shown in FIGS. 1-5, the arm 112 “rests” substantiallyequidistant from the first and second apertures 104 a and 104 b. Boththe first projection 118 a and the second projection 118 b extendpartially into the first and second apertures 104 a and 104 brespectively to retain first and second screws 200 a and 200 b withinthe apertures 104 a and 104 b. From the rest position, the retentionmechanism 106 may be toggled to a first toggled position and a secondtoggled position as discussed below.

Referring now to FIG. 5, a portion of the retention mechanism 106 b ofFIG. 2, and more particularly the first projection 118 a is shown ingreater detail. The first projection 118 a extends through a mouth 120in the opening 110 and into the first aperture 104 a. The mouth 120provides communication between the opening 110 and the aperture 104 a.The first projection 118 a may include a top surface 122 thatsubstantially conforms to a top surface 123 of the plate 100. The firstprojection 118 a may include a taper 124 that decreases in thicknessfrom the top surface 122 to a tip 126 on the distal end of the firstprojection 118 a. The taper 124 may facilitate engagement with the screw200 as illustrated in FIGS. 6A-6D.

Referring now to FIGS. 6A-6D, engagement between the screw 200 and theretention mechanism 106 are shown in greater detail. The screw 200includes a head 202 and a threaded shaft 204. The head 202 may be drivenby a screwdriver such that the shaft 204 penetrates the vertebra (notshown) to secure the plate 100. In FIG. 6A, the screw 200 is insertedinto the first aperture 104 a. As the screw 200 advances through thefirst aperture 104 a, a bottom surface 206 of the head 202 moves towardsthe retention mechanism 106. As the head 202 is driven, the shaft 204engages more of the vertebra, and the bottom surface 206 begins tocontact the taper 124 of the first projection 118 a as shown in FIG. 6B.The bottom surface 206 exerts a downward force on the retentionmechanism 106. The downward force pushes against the taper 124 whichtransfers a portion of the downward force to the retention mechanism106. The flexible arm 112 (not shown) bends due to the force, and theprojection 118 a begins to move away from the first aperture 104 a, asillustrated in detail in FIG. 6B.

Continuing now with FIG. 6C, as the screw 200 continues to be driveninto the vertebra, the bottom surface 206 passes by the taper 124 and aside wall 208 of the head 202 contacts the tip 126 of the projection 118a. At this point, the retention mechanism 106 is in the first toggledposition. In a toggled position, the arm 112 of the retention mechanism106 may be fully bent towards the opposing aperture as will be discussedin detail below. The screw 200 continues to be driven into the vertebrauntil fully seated in FIG. 6D. Once the screw 200 is fully seated, theretention mechanism 106 returns to the rest position. Now, the tip 126of the projection 118 a extends over a top surface 210 of the head 202of the screw 200 and the bottom surface 206 may contact a lip 127 in theaperture 104 a. Thus, the retention mechanism 106 prevents the screw 200from backing out from the plate 100. Although the top surface 210 of thescrew 200 contacts the projection 118 a in FIG. 6D, a gap may remainafter the screw 200 attaches to a vertebra. As can be seen in FIG. 6D, agap 128 may remain between the projection 118 a and the side wall 208 ofthe screw 200 once the retention mechanism 106 has returned to the restposition. The gap 128 permits the retention mechanism 106 to bendtowards the first aperture 104 a when the second screw 200 b is insertedinto the second aperture 104 b as discussed below with reference toFIGS. 7A-7E.

Referring now to FIGS. 7A-7E, the bone fixation system and method areshown in greater detail by a series of partial top views. In FIG. 7A, afirst half of the plate 100 is shown positioned over the first vertebra300. The retention mechanism 106 is in the rest position with no screwsin place. In FIG. 7B, the first screw 200 a is inserted into the firstaperture 104 a and driven into the vertebra 300. As described withrespect to FIGS. 6B-C, the bottom surface 206 of the screw 200 acontacts the taper 124 causing the retention mechanism 106 to bend aboutthe proximal end 114 of the arm 112. The arm 112 elastically bends tothe first toggled position before the first screw 200 a is fully seatedin the first aperture 104 a. In FIG. 7C, the first screw 200 a is fullyseated in the first aperture 104 a. The retention mechanism 106 returnsto the rest position to prevent the first screw 200 a from backing awayfrom the plate 100. The tip 126 of the projection 118 a extends over thetop surface 210 of the screw head 202, as shown in FIG. 6D. Thus, thescrew head 202 is locked between the projection 118 a and the lip 127.

Referring now to FIG. 7D, the second screw 200 b is inserted into thesecond aperture 104 b and driven into the vertebra 300. As describedwith respect to FIGS. 6B-C, the bottom surface 206 of the screw 200 bcontacts the taper 124 on the distal end of the projection 118 b causingthe retention mechanism 106 to bend about the proximal end 114 of thearm 112. The arm 112 elastically bends to the second toggled positionbefore the second screw 200 b is fully seated in the second aperture 104b. In FIG. 7E, the second screw 200 a is fully seated in the secondaperture 104 b. The retention mechanism 106 returns to the rest positionto prevent the second screw 200 b from backing away from the plate 100.The tip 126 of the projection 118 b extends over the top surface 210 ofthe screw head 202 of the second screw 202 b. Thus, the screw head 202is locked between the projection 118 b and a corresponding lip 127 ofthe second aperture 104 b.

FIGS. 8 and 9 illustrate another embodiment of a bone fixation plate 800that includes separate retention mechanisms 806 a-d (collectivelyretention mechanisms 806) for each aperture 804 a-d (collectivelyapertures 804). For example, a first retention mechanism 806 a isdisposed between first and second apertures 804 a and 804 b and isconfigured to prevent a first screw (not shown) in the first aperture804 a from backing out of the plate 800 after fixation to a vertebra.The first retention mechanism 806 a may be molded or machined from thematerial of the plate 800. Thus, the first retention mechanism 806 a maybe integral and continuous with the plate 800. In other embodiments, thefirst retention mechanism 806 a may be attached to the plate 100 betweenthe apertures 804 a and 804 b. The first retention mechanism 806 a maybe attached by welding, snap fit, friction welding, or other forms ofattachment. A second retention mechanism 806 b is disposed between thesecond aperture 804 b and the first retention mechanism 806 a and isconfigured to prevent a second screw (not shown) in the second aperture804 b from backing out of the plate 800 after fixation to the vertebra.

For simplicity, two retention mechanisms and one pair of adjacentapertures are discussed in detail herein. However, it is understood byone in the art that the plate 800 of the present disclosure may includetwo retention mechanisms disposed between any pair of apertures. Forexample, third and fourth apertures 804 c and 804 d may be mirror imagesof the first and second apertures 804 a and 804 b and configured toreceive third and fourth screws, respectively. Similarly, a thirdretention mechanism 806 c, may be disposed between the third and fourthapertures 804 c and 804 d and a fourth retention mechanism 806 d may bedisposed between the fourth aperture 804 d and the third retentionmechanism 806 c.

Referring now to FIG. 9, a top view of the plate 800 illustratesadditional features of the retention mechanism 806 and apertures 804 aand 804 b. The first aperture 804 a and the second aperture 804 b areformed in one end of the plate 100. The first and second apertures 804 aand 804 b may be substantially circular and configured to receive thebone screws 200 a and 200 b respectively (not shown), similar toapertures 104 a and 104 b as shown in FIG. 2. Each retention mechanism806 is disposed in a separate opening 810 formed around each retentionmechanism 806. The openings 810 may be irregular-shaped to conform tothe geometry of the retention mechanism 806. In one embodiment, eachopening 810 may be in communication with a neighboring aperture 804.That is, a continuous wall is shared between one aperture, such asaperture 804 a and one opening 810.

Each retention mechanism 806 extends from the plate 800 into the opening810 and is configured to lock one bone screw to the plate 800. Theretention mechanism 806 includes a flexible arm 812 extending from theplate 800 into the opening 810. The flexible arm 812 may be attached tothe plate at a proximal end 814 and include a distal end 816cantilevered in the opening 810. A projection 818 extends from thedistal end 816 through the opening 808 and towards the aperture 804.Thus in the present embodiment, the retention mechanism 806 may resemblea “J” shaped geometry or a cane. For example, the projection 818 mayinclude curvature having a radius equivalent to the length of the arm812 from the proximal end 814 to the distal end 816.

The retention mechanisms 806 function similar to the retention mechanism106 as depicted in FIGS. 6A-6D. That is, each retention mechanism 806includes a taper on the projection 818 that comes in contact with abottom surface of a screw when the screw is driven into a vertebra. Asthe screw is driven further into the vertebra, the retention mechanism806 contacts an outer wall of the head of the screw and moves from arest position to a toggled position. However, in the present embodiment,each retention mechanism 806 locks one screw rather than two screws asretention mechanism 106. Thus, the retention mechanism 806 in thepresent example may be toggled between the rest position as depicted inFIGS. 8 and 9 and one toggled position similar to the first toggledposition of the retention mechanism 106.

Example embodiments of the methods and systems of the present inventionhave been described herein. As noted elsewhere, these exampleembodiments have been described for illustrative purposes only, and arenot limiting. Other embodiments are possible and are covered by theinvention. Such embodiments will be apparent to persons skilled in therelevant art(s) based on the teachings contained herein. Thus, thebreadth and scope of the present invention should not be limited by anyof the above-described exemplary embodiments, but should be defined onlyin accordance with the following claims and their equivalents.

The invention claimed is:
 1. A method for bone fixation comprising: inserting a first screw into a first aperture of a plate to secure the plate to a vertebra; advancing the first screw to elastically deform a retention member formed in an opening of the plate, wherein the opening is in communication with the first aperture; elastically deforming the retention member from a rest position to a first toggled position; and advancing the first screw until the retention member elastically returns to the rest position.
 2. The method of claim 1, wherein elastically deforming the retention member from the rest position to the first toggled position includes flexing an arm of the retention member.
 3. The method of claim 1, wherein advancing the first screw to elastically deform the retention member includes contacting a projection of the retention member with a head of the first screw.
 4. The method of claim 1, further comprising: inserting a second screw into a second aperture of the plate; advancing the second screw to elastically deform the retention member formed in the opening of the plate, wherein the opening is in communication with the second aperture; elastically deforming the retention member from the rest position to a second toggled position; and advancing the second screw until the retention member elastically returns to the rest position.
 5. The method of claim 4, wherein the first aperture and the second aperture are partially blocked when the retention member is in the rest position and one of the first and second apertures is partially blocked when the retention member is in one of the first toggled position and the second toggled position. 